Miniature switch having indicating means

ABSTRACT

The movement of a pushbutton or of a knob causes a ball to be pressed against a tensed flat, ferromagnetic spring attracted to a permanent magnet, forcing the spring, which carries the movable break and make contacts, away from the magnet and to snap close the make contacts, the stationary one of which is mounted on a plate with conductive paths. When the ball is released, the magnet attracts the spring and snaps the switch back to its rest position.

United States Patent Inventor Jean C. Viau Basel, Switzerland Appl. No.833,347

Filed June 16, 1969 Patented July 20, 1971 Assignee Sibalco W. Siegrist8: Co.

Basel, Switzerland Priority June 29, 1968 Switzerland 9741/68 MINIATURESWITCH HAVING INDICATING MEANS 12 Claims, 6 Drawing Figs.

[15. Cl 200/167 A, 200/67 1nt.Cl 110lh 9/18 Field of Search 200/67 F,

[56] References Cited UNITED STATES PATENTS 2,985,734 5/1961 Howell etal ..200/67 (F) (X) 3,292,123 12/1966 Siklos 335/205 3,447,110 5/1969Dotto. ..200/67 (F) (X) 3,486,144 12/1969 Paige ..200/67 (F) (X) PrimaryExaminer-H. 0 Jones AnomeyKarl F. Ross ABSTRACT: The movement of apushbutton or of a knob causes a ball to be pressed against a tensedflat, ferromagnetic spring attracted to a permanent magnet, forcing thespring, which carries the movable break and make contacts, away from themagnet and to snap close the make contacts, the stationary one of whichis mounted on a plate with conductive paths. When the ball is released,the magnet attracts the spring and snaps the switch back to its restposition.

PATENTED M20 1911 saw 2 or 2 Fig.5

Jean-Claude Vi Inventor Attorney MINIATURE SWITCH HAVING INDICATINGMEANS Components in the field of electrical engineering are constantlybeing reduced in size. Among these are pushbutton switches of all kindsand rotary switches, which are usually mounted on switching orinstrument panels and comprise a cylindrical housing with a mountingnut, a pushbutton or a rotatable knob, and the switch proper.Momentary-contact pushbutton switches are (if normally open) closed onlyas long as the button is depressed, the switch returning to its restposition as soon as the button is released. Pushbutton switches of thiskind are principally used to switch in automatically operating circuits.In some applications, it makes no difference that the contacts make openand close slowly, but in other applications it is essential that thecontacts make and break quickly at all times, even though the button isslowly pressed or released. It is easy to design a momentaiycontactpushbutton switch incorporating a snap action, provided that the latteris not limited as to size. But if the outer dimensions of the switch areto be greatly reduced, it is very difficult to incorporate a snapaction, because the latter is not easily contracted. The samedifficulties appear when designing miniature locking-type pushbuttonswitches and nonreturn rotary switches.

The object of the invention is to provide pushbutton and rotary switchesthat embody a snap action and yet are miniature in size.

I accomplish this object by the features of the invention describedhereinafter with reference to the accompanying drawing wherein:

FIG. 1 is a greatly enlarged longitudinal section of one embodiment;

FIG. 2 is a greatly enlarged longitudinal section of a secondembodiment,

FIGS. 3 and 4 are elevational views of the respective faces of the plateof the switch shown in FIG. 2;

FIG. 5 is a greatly enlarged longitudinal section of the switch shown inFIG. 2 modified for rotary operation; and

HO. 6 is a view taken along line Vl-Vl of FIG. 5. i

With reference to FIG. 1, the miniature switch includes a cylindricalhousing 11 having a flange 12 and screw threads 13 with a nut 14 formounting the switch on a panel. An electrically conductive plate 15,arranged in the axial plane of the switch, is fixed in the housing 11 bytwo socket parts 16 and 17, each having a respective pin 18 and 19 thatprojects into a corresponding opening in the plate 15. Both socket partsare cylindrical and have a shoulder 20, one side of which contacts ashoulder 21 of the housing and the other side of which is held by aflange 22 of the housing. The two socket parts 16 and 17 can beidentical, provided that the pins 18 and 19 are relatively offset in thetransverse direction and not, as shown in FIG. I, in the longitudinaldirection. The conductive plate projects beyond the socket parts,enabling leads to be connected thereto.

One end of the socket parts terminates in a thin-walled collar-23, whichextends into the housing 11. Between the collar and the wall of thehousing is disposed a coil spring 24 supported by the shoulder 21. Asleeve 25, which ends in a switching cam 26, is slidably arranged in thehousing and rests on the spring 24. Another sleeve 27, which has ashoulder 28 that cooperates with the housing flange 12 to act as a stop,carries on its free end a transparent or translucent pushbutton 30 heldin a metallic collar 29. The inner end of the sleeve 27 contacts thesleeve 25' and incorporates an annular recess 31 holding a snapring 32,which engages a groove (not shown) in the conductive plate 15 and holdsthe sleeve 27 in the housing. The width of the recess 31 determines thestroke of the sleeve 27.

The front end of the plate 1-5 carries a socket 33 for an incandescentor glowlamp 34 whose light is visible through the pushbutton 30QA snapswitch, having a flat steel spring 35 as the movable contact, is mountedon the conductive plate 15. The two faces of this flat spring areprovided with respective contacts 36 and 37 separated by a bent,generally Z-shaped extremity 38 which projects through an opening 39 inthe plate 15, each contact confronting respective side of the plate 15.The contact 36 and a stationary contact 40 on the plate 15 constitutethe break contacts while the contact 37 together with another stationarycontact 41 on the plate 15 form the make contacts. A rivet 42 fixes thespring 35 to the conductive plate 15, there being placed underneath therivet head a washer 43 with a bent-up rim, to prevent the spring 35 frombending permanently at the edge of the rivet head. A permanent magnet 44is held in an opening in the plate 15, attracting the steel spring 35which acts as its armature. A ball 45 is loosely held between the magnet44 and the rivet 42 in an opening of theplate 15 by an edge 46 of theplate face remote from the spring 35. Since the ball extends beyond thisedge, the cam 26 presses it against the spring 35 when the pushbutton 30is pushed in. The snap action of the contacts results from the fact thatthe inherent bias of the ferromagnetic spring 35, once the latter ispushed away from the magnet 44 by the ball 45, suddenly snaps the switchto its closed position, in which the contacts 37 and 41 touch. When thepushbutton is released, the magnetic attraction suddenly draws thespring back and snaps the switch open.

Both faces of the plate are provided with an electrically conductivelayer or plating. The stationary contacts 40 and 41 are advantageouslyformed by these layers or platings.

The embodiment of the miniature switch shown in FIG. 2 has a cylindricalhousing 51 composed of front and rear parts of different diameters. Tomount the switch on a panel the housing has a flange 52 and a screwthread 53 with a nut 54. A plate 55, arranged along the axial plane ofthe housing 51, is fixed in the housing by the socket parts 56 and 57 ofa twopiece, electrically insulating, essentially cylindrical sleeve 58which is held in the housing and contacts the inside face thereof. Tofix the plate 55 in place, and especially to prevent .it from shiftingaxially, each socket part 56 and 57 comprises a respective pin thatprojects into a corresponding opening in the plate. To preserve thesimplicity of FIG. 2, a single pin 59 (that of the socket part 56) andone hole 60 of the plate 55 are shown in the plane of the Figure.Actually, the plate has two holes 60, one on each side of the sectionalplane, as can be seen in FIGS. 3 and 4 (in which the pins 59 arereferenced). The longitudinal edges of the plate 55 are held incorresponding grooves (not shown) along the longitudinal edges of thetwo-piece sleeve 58. The plate 55 extends beyond the socket parts 56 and57 to expose the conductors of the plate.

The portion of the sleeve 58 adjoining the socket parts 56 and 57 issqueezed by the wall of the housing 51. A collar 61 of the sleeve 58rests on a shoulder 62 of the housing 51 and determines the longitudinalposition of the sleeve with respect to the housing when the former isforced in. The part of the sleeve 58 located above the collar 61 formsan annular gap 63 with the inside face of the wall of the housing 51.The sleeve 58 is provided, oppositeone face of the plate 55, with around opening 64 from which a tubular collar 65 extends to the plate 55.

A sleeve 66 is slidably arranged in the housing 51 and has a shoulder 67that cooperates with the flange 52 to act as a stop. A snapring 68 heldin an annular groove of the flange 52 limits movement of the sleeve 66in the opposite direction. An annular projection 90, whose significancewill be described below, may be omitted in this embodiment. A helicalcompression spring 69, bearing from below upon an upper shoulder of thesleeve 66, urges the sleeve 66 outwardly and causes another shoulder topress against the snapring 6 8. The inner end of the spring 69 issupported by an electrically insulating disc 70 having a central holethrough which projects an incandescent or glowlamp 71. Alternatively,the housing can support the rear end of the spring 69. The base of thelamp presses against contacts mounted on the plate 55. These contacts,now shown in FIG. 2, will be explained in connection with FIGS. 3 and 4.The free end of the sleeve 66 carries a transparent or translucentpushbutton 73 held in a metallic collar 72. The rear end of the sleeve66 terminates in a thin-walled collar 74 which, when the pushbutton 73is pressed in, moves between the inside face of the housing 51 and aball 76 which is held in the tubular collar 65 and projects into anopening 75 of the plate The construction of the plate 55, which is madeof an electrically insulating material, is shown in FIGS. 2, 3 and 4.Rivets 79 mount two lamp contacts 77 and 78 on the front end of theplate 55. The contact 77 resiliently engages the base of the lamp 71,whereas the other contact 78 makes a connection with the central basecontact of the lamp pressed thereagainst by the spring 69. Twoconductive lines 80 and 8| (FIG. 4) connect the contacts 77 and 78 withrespective terminal holes 82 and 83 which are located in the part of theplate 55 projecting beyond the housing SI.

As in the previous embodiment, there is mounted on the plate 55 a snapswitch whose parts are denoted by the same reference numerals since itis essentially the south as the snap switch shown in FIG. 1. The switchcomprises, as before, a flat steel spring 35 fixed by a rivet 42 to theplate 55. The spring, having the two contacts 36 and 37, serves as themovable element. The mobile contact 36 and the stationary contacts 40 onthe plate 55 are the break contacts, whereas the mobile contact 37 andthe stationary contact 41 on the plate 55 are the make contacts. Thepermanent magnet 44, held in an opening of the plate 55, consists of twopieces in this embodiment. The surfaces of these pieces directlyopposite the spring 35 are respectively north and south poles.

As previously explained the plate 55 has an opening 75 that receives theball 76. When the pushbutton 73 is depressed, the collar 74 is pushedbetween the inside face of the housing wall and the ball 76, camming thelatter against the spring 35. The snap action of the contacts resultsfrom the fact that the bias of the spring 35, once the latter (acting asthe magnet armature), is pushed away from the magnet 44 by the ball 76,snaps the switch contacts from the rest position, shown in FIG. 2, tothe closed position, in which the make contacts 37 and 41 are closed.When the pushbutton is released, the magnetic attraction suddenly drawsthe spring back and snaps the break contacts 36 and 40 closed.

As shown in FIGS. 3 and 4, each face of the plate 55 is provided with anelectrically conductive layer of plating which forms the stationarycontacts 40 and M of the snap switch and establishes conductive paths84, 85 and 86 for connecting these stationary contacts and the spring 35to the respective terminal holes 87, 88 and 89.

Burned out lamps 7I are easily replaced by pulling the pushbutton 73 andthe sleeve 66 out of the housing 51 against the holding force of thesnapring 68. Since the assembly composed of the lamp 7I, disc 70 andspring 69 is loose, a fresh lamp is easily inserted without tools andthen fixed behind the snapring 68 by pushing in the sleeve 65 until thelatter is held by the snapring, as shown in FIG. 2.

The switch shown in FIG. 2 is a momentary-contact switch automaticallyreturning to its rest position when the pushbutton is released. A simplemodification converts the switch into one of the locking type remaininglocked in its make position until the pushbutton is pulled out. To thisend, the front end of the sleeve 66 is provided behind the shoulder 67with a detent constituted by the aforementioned annular projection 90having sloping flanks as shown in FIG. 2. When the pushbutton 73 isdepressed, the projection 90 presses on the snapring 68 and forces itradially outward until the projection is positioned underneath thesnapring, whereupon the latter contracts to its original diameterhwhenthe pushbutton 73 is released, the snapring prevents the sleeve 66 fromreturning to its original position, even though the spring 69 pressesthe projection 90 against the snapring. The make contacts 37 and 41remain closed. The switch is returned to its rest position by pullingout the pushbutton 73, so that the sloping front flank of the projection90 slides past the snapring.

FIGS. and 6 show a modification that converts the embodiment illustratedin FIG. 2 into a rotary switch. The switch shown in FIG. 5 differs fromthat shown in FIG. 2 in that the shoulder 91 of the sleeve 92 (replacingthe sleeve 66 of the preceding embodiment) is sufficiently. lengthenedso as to be i in contact at all times with the flange 52 and thus toprevent longitudinal movement of the button or knob 72, 73. Instead ofthis construction, the sleeve 92 can incorporate an annular groove, thesnapring 68 then partly lying in the groove of the flange 52 and partlyin the groove of the sleeve 92 to prevent longitudinal movement of thelatter. Further, a thin-walled collar 93 is lengthened rearwardly, ascompared to the collar 74. The collar 93 is provided along itscircumference with an opening 94 whose center lies along a transverseline common to it and to the center of the ball 76, whereby the ballprojects into this opening. The remaining parts of the switch correspondto those of the switch shown in FIG. 2. If the knob 72 and 73 and thusits sleeve 92 are rotated, the collar 93 earns the ball 76 out of theopening 94, pressing the ball against the spring 35 which is thusdisengaged from the magnet 44 and snapped into its make position, aspreviously described in connection with FIG. 2. A further opening (notshown), offset by, for example 60 from the opening 94, and of aconsiderably smaller diameter, can be provided in the collar'93 toensure that a definite rotary displacement of the knob corresponds tothe make position of the switch. When the knob is turned to thisposition, the ball 76 snaps into this smaller opening while stillpreventing the spring 35 from snapping back to the rest position. Thespring is free to do this only after the knob has been turned forward orbackward until the ball 76 is again edges of each part of the two-pieceinsulating sleeve 58 with'a respective shoulder 95 which contacts theinside face of the housing 51. The rotary sleeve 92 has two longitudinalslots 96 whose arcuate length corresponds to the desired rotationalmovement of the knob. The edges of the slots 96 together with theshoulders 95 constitute the stops for the rest and make positions of therotary switch shown in FIG. 5.

In all the described embodiments of the invention, the switch isconstructed as a single-pole switch with make and break contacts. Inaccordance with the invention, the switch can also be constructed withtwo or more poles. For example, in the embodiment illustrated in FIGS.2, 3, and 4, two flat springs 35 with contacts can be fixedside-by-side, and insulated from each other, on the plate 55. A paireach of the stationary contacts 40 and 41, together with theirconnecting conductive paths, then provided side-by-side, and insulatedone from the other, on this plate. A single ball 45 can be provided foroperating both springs 35, the ball pressing on both springs through anelectrically insulating crossbar interconnecting these springs.

A switch withthe snap arrangement of the invention can be made verysmall without adversely affecting either its dependability or itsoperating life. A switch of the kind shown in FIG. 2 has been madehaving an overall length of about 50 mm., including the lamp 71 and theplate 55, and a maximum diameter of II mm.

Although several preferred embodiments of the invention have beendescribed, the scope of, and the breadth of protection afforded to, theinvention are limited solely by the appended claims.

lclaim:

I. A miniature switch comprising a substantially in the form ofa hollowcylindrical body, a plate positioned in said housing and extending alongthe longitudinal axis thereof, at least one flat ferromagnetic springsubstantially extending along the longitudinal axis of said housing,fastening means fixedly securing one end of said flat spring to one endportion of said plate, said flat spring having a portion movable in adirection transverse to the longitudinal axis of said housing, saidmovable portion and said plate provided with at least one pair ofconfronting electrical contacts, a magnet fixedly secured to said plate,one face of said magnet adjoining said movable portion for holding saidflat spring in a first position against an inherent transverse biasingforce of said flat spring, a ball positioned in said housing betweensaid magnet and said fastening means in line with the plane of saidplate, said ball bearing on one side of said plane against said movableportion, movable actuating means arranged of one end of said housingnear said one end portion of said plate and extending into said housingfor pressing said ball against said movable portion to free the latterfrom said magnet and to displace said movable portion into a secondposition upon operation of said actuating means, and a plurality ofsocket parts engaging an opposite end portion of said plate fixing saidplate in said housing at the end thereof remote from said actuatingmeans.

2. A switch as defined in claim 1 wherein said movable portion of saidflat spring includes a generally Z-shaped extremity, said plate havingan opening traversed by said extremity, the latter provided on eachlongitudinal side with a mobile electrical contact confronting arespective face of said plate, each face of said plate provided with arespective stationary electrical contact cooperating with a respectiveone of said mobile contacts whereby in said first position of saidmovable portion one of said mobile contacts engages one of saidstationary contacts whereas in said second position of said movableportion the other of said mobile contacts engages the other of saidstationary contacts.

3. A switch as defined in claim 2 wherein said opposite end portion ofsaid plate projects beyond the end of said housing remote from saidactuating means, said plate provided with electrically conducting pathsfor connecting said mobile and stationary contacts to the exposed partof said opposite end portion.

4. A switch as defined in claim 1 wherein said actuating means is apushbutton, further comprising a first sleeve connected with saidpushbutton for displacement thereby from a rest position in the axialdirection of said housing, a coil spring axially spaced from said firstsleeve and axially supported in said housing, a second sleeve interposedbetween said coil spring and said first sleeve for joint displacementwith said first sleeve against the force of said coil spring, and a camon said second sleeve for pushing said ball against said movable portionof said flat spring in response to axial movement of said sleeves fromthe rest position, said plate having an opening loosely receiving saidball and a retaining edge on the face of said plate remote from saidflat spring for preventing said ball from falling out of said opening.

5. A switch as defined in claim 1 wherein said actuating means is amovable rigid knob with a sleeve extending into said housing, said balladjoining an inside wall surface of said housing, a free end of saidsleeve remote from said knob projecting between said ball and said innerwall surface for camming said ball against said movable portion of saidflat spring upon inward movement of said sleeve by said knob, saidsleeve having a shoulder at the end thereof adjacent'said movable knob;further comprising a helical compression spring within said sleevebearing at its one end against said shoulder and at its other end,remote from said knob, against said housing, and stop means for limitingthe axial movement of said knob.

6. A switch as defined in claim 5 wherein said knob is a pushbutton,further comprising detent means for releasably locking said pushbuttonin a depressed position.

7. A switch as defined in claim 5, comprising a further sleeve integralwith said socket parts and in contact with the inner surface of saidhousing, said further sleeve having an aperture receiving said ball, anda collar centered on said aperture extending from said opening andsurrounding said ball.

8. A switch as defined in claim 5 wherein said knob is rotatable and hasan opening receiving said ball whereby-rotation of said knob and sleevecams said ball out of said opening and against said movableportion ofsaid flat spring.

9. switch as defined in claim 8 wherein a urt er sleeve mtegral withsaid socket parts and in contact with the inner surface of said housingis provided with an aperture receiving said ball and with a collarcentered on said aperture and extending therefrom around said ball, thefirst-mentioned sleeve having at least one longitudinal slot coactingwith and at least one longitudinal shoulder on said further sleeve forlimiting rotation of said knob.

10. A switch as defined in claim 1, further comprising a lamp mounted onsaid one end portion of said plate, said actuating means having alight-transmissive wall for making visible the light of said lamp, saidplate provided with conductive paths leading to said opposite endportion thereof for supplying current to said lamp.

11. A switch as defined in claim 10 wherein said actuating means is amovable knob rigid with a sleeve and wherein said ball adjoins an innerwall surface of said housing, an end of said sleeve remote from saidknob projecting between said ball and said inner wall surface forcamming said ball against said movable portion of said flat spring upondisplacement of said sleeve by said knob, said sleeve having a shoulderat the end thereof adjacent said knob; further comprising a helicalcompression spring within said sleeve bearing at one end against saidshoulder, stop means for limiting the axial movement of said knob, andan electrically insulated disc mounted within said sleeve and supportingthe other end of said helical spring, said disc having a central openingfor holding the base of said lamp in contact with further electricalcontacts on an end of said plate to complete an electrical circuitthrough said base.

' 12. A switch as defined in claim I wherein said magnet is of thepermanent type.

1. A miniature switch comprising a substantially in the form of a hollowcylindrical body, a plate positioned in said housing and extending alongthe longitudinal axis thereof, at least one flat ferromagnetic springsubstantially extending along the longitudinal axis of said housing,fastening means fixedly securing one end of said flat spring to one endportion of said plate, said flat spring having a portion movable in adirection transverse to the longitudinal axis of said housing, saidmovable portion and said plate provided with at least one pair ofconfronting electrical contacts, a magnet fixedly secured to said plate,one face of said magnet adjoining said movable portion for holding saidflat spring in a first position against an inherent transverse biasingforce of said flat spring, a ball positioned in said housing betweensaid magnet and said fastening means in line with the plane of saidplate, said ball bearing on one side of said plane against said movableportion, movable actuating means arranged of one end of said housingnear said one end portion of said plate and extending into said housingfor pressing said ball against said movable portion to free the latterfrom said magnet and to displace said movable portion into a secondposition upon operation of said actuating means, and a plurality ofsocket parts engaging an opposite end portion of said plate fixing saidplate in said housing at the end thereof remote from said actuatingmeans.
 2. A switch as defined in claim 1 wherein said movable portion ofsaid flat spring includes a generally Z-shaped extremity, said platehaving an opening traversed by said extremity, the latter provided oneach longitudinal side with a mobile electrical contact confronting arespective face of said plate, each face of said plate provided with arespective stationary electrical contact cooperating with a respectiveone of said mobile contacts whereby in said first position of saidmovable portion one of said mobile contacts engages one of saidstationary contacts whereas in said second position of said movableportion the other of said mobile contacts engages the other of saidstationary contacts.
 3. A switch as defined in claim 2 wherein saidopposite end portion of said plate projects beyond the end of saidhousing remote from said actuating means, said plate provided withelectrically conducting paths for connecting said mobile and stationarycontacts to the exposed part of said opposite end portion.
 4. A switchas defined in claim 1 wherein said actuating means is a pushbutton,furtHer comprising a first sleeve connected with said pushbutton fordisplacement thereby from a rest position in the axial direction of saidhousing, a coil spring axially spaced from said first sleeve and axiallysupported in said housing, a second sleeve interposed between said coilspring and said first sleeve for joint displacement with said firstsleeve against the force of said coil spring, and a cam on said secondsleeve for pushing said ball against said movable portion of said flatspring in response to axial movement of said sleeves from the restposition, said plate having an opening loosely receiving said ball and aretaining edge on the face of said plate remote from said flat springfor preventing said ball from falling out of said opening.
 5. A switchas defined in claim 1 wherein said actuating means is a movable rigidknob with a sleeve extending into said housing, said ball adjoining aninside wall surface of said housing, a free end of said sleeve remotefrom said knob projecting between said ball and said inner wall surfacefor camming said ball against said movable portion of said flat springupon inward movement of said sleeve by said knob, said sleeve having ashoulder at the end thereof adjacent said movable knob; furthercomprising a helical compression spring within said sleeve bearing atits one end against said shoulder and at its other end, remote from saidknob, against said housing, and stop means for limiting the axialmovement of said knob.
 6. A switch as defined in claim 5 wherein saidknob is a pushbutton, further comprising detent means for releasablylocking said pushbutton in a depressed position.
 7. A switch as definedin claim 5, comprising a further sleeve integral with said socket partsand in contact with the inner surface of said housing, said furthersleeve having an aperture receiving said ball, and a collar centered onsaid aperture extending from said opening and surrounding said ball. 8.A switch as defined in claim 5 wherein said knob is rotatable and has anopening receiving said ball whereby rotation of said knob and sleevecams said ball out of said opening and against said movable portion ofsaid flat spring.
 9. A switch as defined in claim 8 wherein a furthersleeve integral with said socket parts and in contact with the innersurface of said housing is provided with an aperture receiving said balland with a collar centered on said aperture and extending therefromaround said ball, the first-mentioned sleeve having at least onelongitudinal slot coacting with and at least one longitudinal shoulderon said further sleeve for limiting rotation of said knob.
 10. A switchas defined in claim 1, further comprising a lamp mounted on said one endportion of said plate, said actuating means having a light-transmissivewall for making visible the light of said lamp, said plate provided withconductive paths leading to said opposite end portion thereof forsupplying current to said lamp.
 11. A switch as defined in claim 10wherein said actuating means is a movable knob rigid with a sleeve andwherein said ball adjoins an inner wall surface of said housing, an endof said sleeve remote from said knob projecting between said ball andsaid inner wall surface for camming said ball against said movableportion of said flat spring upon displacement of said sleeve by saidknob, said sleeve having a shoulder at the end thereof adjacent saidknob; further comprising a helical compression spring within said sleevebearing at one end against said shoulder, stop means for limiting theaxial movement of said knob, and an electrically insulated disc mountedwithin said sleeve and supporting the other end of said helical spring,said disc having a central opening for holding the base of said lamp incontact with further electrical contacts on an end of said plate tocomplete an electrical circuit through said base.
 12. A switch asdefined in claim 1 wherein said magnet is of the permanent type.